Judging from all your screenshots, they’re all showing that you’re limited by MainThread, this means you have a CPU bottleneck, but it may not be the bottleneck that you think because your CPU is powerful enough.
I stumbled upon this topic before when I had the same Limited by MainThread issue as you do, and following the advice there actually helped my FPS to be restored with no more stuttering too. I thought this workaround is no longer needed after SU5. But give it a try, maybe it helps your case as it did mine.